In engines utilizing a prechamber, also referred to as a pre-combustion chamber, the prechamber is generally provided in a cylinder head of the engine. The prechamber is in fluid communication with the main chamber of a cylinder in the engine. A pilot charge of fuel and air is introduced into the prechamber. Combustion commences in the prechamber, and proceeds from the prechamber to the main chamber to combust a main charge of fuel and air. Engines utilizing prechambers may achieve high compression ratios and power output, however during operation, the temperature in the prechamber can exceed the temperature in the main chamber.
Japanese patent publication JP2015055185A to Toho Gas KK discloses a gas engine having a combustion chamber. A plug cover forms an ignition chamber in the combustion chamber. The plug cover has multiple communication ports that allow the ignition chamber to communicate with the combustion chamber. An ignition plug is provided in the ignition chamber to initiate combustion. An exhaust passage, controlled by an exhaust valve, opens into the ignition chamber for exhausting hot combustion gases therein to improve durability of the ignition plug.